The invention relates to an anti-corrosive coating compound with metal particles, a method for producing this coating compound and a workpiece coated with this coating compound.
Coating compounds, which act in an anti-corrosive manner and which contain metal particles, are generally known, e.g. from WO 2005/090 502. They primarily contain metal particles for the cathodic corrosion protection, for the most part zinc and/or aluminum particles or zinc alloy particles as well as binders in the presence of water and/or solvents. The binders are often based on silicon-containing compounds; typical binders are inorganic mono-, oligo- or polymers such as silicates, silanes or silanols, but also siloxanes. Depending on the intended use, also organic binders, if applicable also as co-polymers of the inorganic binders, are suitable.
While the coating compounds often offer good corrosion protection after hardening on a workpiece, their stability during use is often problematic since some of the aforementioned components react with the liquid of the coating compound or with the workpieces to be coated. Due to the insertion and extraction of workpieces from an immersion bath, impurities can also be introduced so that undesirable secondary reactions, which reduce the service life of the immersion bath, can occur during the coating. Without a stabilizer, which prevents these undesirable secondary reactions, the service life of a coating compound is often just a few hours. A preparation for a coating compound, e.g. for a coil-coating process, should be usable for at least 48 hours without quality loss, a preparation for an immersion bath a week or more, if possible.
Up until now, boric acid or another boron-containing compound was used to stabilize coating compounds containing metal particles. Due to toxicological concerns with respect to boron compounds and legal requirements, this will no longer be possible in the future.